Coarse Woody Debris as a Land Reclamation Amendment at an Oil Sands Mining Operation in Boreal Alberta, Canada

Effects of Coarse Woody Debris on Soil Temperature and Water Content in Two Reconstructed Soils in Reclaimed Boreal Forest

Coarse woody debris (CWD) and cover soils are used to expedite ecological processes in reclaimed boreal forests after oil sands mining. Soil water content and soil temperature are considered key factors for revegetation during mine reclamation as they impact soil surface and atmosphere interactions and plant growth. However, the effects of CWD and cover soils on soil water content and temperature are not well studied. This study assessed the impact of CWD size (large, small) and type (spruce: Picea mariana, aspen: Populus tremuloides) on soil water content and temperature in two soils constructed with forest floor-mineral mix (FMM) and peat-mineral mix (PMM)) at oil sands reclamation sites. Annual and summer precipitation showed year-to-year variability; mean air temperature did not. Soil cover type had a greater impact on moderating soil water content than CWD, with PMM having a stronger influence on water content and temperature than FMM. Adding CWD increased soil water content more in FMM than PMM, and the effect on soil temperature was mostly observed during the summer months. In PMM, spruce small CWD was associated with greater water content, whereas there was no distinct differentiation between CWD size and type in FFM. This study suggests application of CWD in FMM would be more beneficial than in PMM for reclamation.

Deadwood Amount at Disturbance Plots after Sanitary Felling

Deadwood is an important component of forests that fulfils many ecosystem functions. The occurrence, amount and spatial distribution of deadwood in forest ecosystems depend on tree species composition, historical development and past management. In this presented study, we assessed the total amount of deadwood, including fine and coarse woody debris at five areas of predominantly broadleaved forests within the University Forest Enterprise of the Technical University in Zvolen, Slovakia that had been disturbed by windstorm Žofia in 2014. Windthrown wood was salvaged between May 2014 and October 2015. In the year 2018, we performed an inventory of deadwood that remained on-site after salvage logging. The mean volume of deadwood recorded at sample plots fluctuated between 35.96 m³/ha and 176.06 m³/ha and mean deadwood coverage values at individual disturbed areas ranged from 7.27 to 17.91%. In the work, we derived several models for the estimation of deadwood volume based on deadwood coverage and/or diameter, which showed that these characteristics are good proxies of deadwood volume. The tests, involving close-range photogrammetry methods for deadwood quantification, revealed that the number of pieces and the coverage of deadwood recorded in photos was significantly lower than the values derived from field measurements.

Drivers of understory species richness in reconstructed boreal ecosystems: a structural equation modeling analysis

Understory vegetation accounts for the most diverse part of the plant community in boreal forests and plays a critical role in stand dynamics and ecosystem functions. However, the ecological processes that drive understory species diversity are poorly understood and largely unexplored for reconstructed boreal ecosystems. The current study explored the relationships between understory species richness and biotic and abiotic factors in sites reclaimed after oil sands mining in northern Alberta, Canada, three and six growing seasons post-reclamation. Reclaimed sites with two main surface soils, forest floor mineral soil mix (FFMM) and peat mineral soil mix (PMM), were used along with post-fire benchmarks. A number of soil physicochemical (including nutrients) and vegetation properties were measured and considered in the a-priori hypothesis framework. Structural equation models (SEM) were used to evaluate the multivariate relationships. In general, the FFMM sites had greater species richness than the PMM sites, even six growing seasons after reclamation. A maximum 254% increase in graminoid and shrub cover was observed on FFMM between year 3 and 6 post-reclamation, whereas a maximum 137% increase in forb and bryophyte cover was recorded on PMM. The post-fire sites showed a significant increase (70%) only in shrub cover. Major driving factors of understory species richness varied among soil types. The SEM revealed a strong interdependency between species richness and soil and vegetation factors on FFMM with a positive control from soil N on species richness. In contrast, on PMM soil nutrients had a negative effect on species richness. Temporal changes in the drivers of species richness were mostly observed on FFMM through a negative vegetation control on species richness. The models and significant causal paths can be used in monitoring changes in understory species relationships in reclaimed sites and in identifying future research priorities in similar systems.